Allan Hobson and Robert McCarley (1977) presented a neurophysilogical model of dreaming, the Activation-Synthesis hypothesis. They hypothesized that dreaming resulted from the interpretation by the cortex of information concerning eye movements and activated brain stem motor pattern generators. They proposed that in REM sleep, the ascending cholinergic PGO (ponto-geniculo-occipital) waves stimulate higher midbrain and forebrain cortical structures, producing rapid eye movements.